Isolated kidney proximal tubules subjected to
hypoxia/reoxygenation (H/R) have incomplete recovery of mitochondrial membrane potential (DeltaPsi(m)) that can be improved, but not normalized, by
ATP in permeabilized cells as measured by
safranin O uptake. In these studies, the mechanisms for the decreased DeltaPsi(m) in the tubules after H/R are further investigated and impairment of the function of the mitochondrial F(1)F(O)-ATPase is assessed. Normoxic control tubules had a small
ATP-dependent component to DeltaPsi(m), but it required low micromolar levels of
ATP, not the millimolar levels needed to support DeltaPsi(m) in tubules de-energized with
rotenone or after H/R. Micromolar levels of
ATP did not improve DeltaPsi(m) after either mild or severe H/R injury. The dependence of DeltaPsi(m) on millimolar levels of
ATP after H/R decreased over time during reoxygenation.
ATP hydrolysis by the
oligomycin-sensitive, mitochondrial F(1)F(O)-ATPase was well preserved after H/R as long as Mg(2+) was available, indicating that function of both the F(1)F(O)-ATPase and of the
adenine nucleotide translocase, which delivers
nucleotides to it, are largely intact. However,
ATP hydrolysis by the
ATPase did not restore DeltaPsi(m) as much as expected from the rate of
ATP utilization. These findings, taken together with the observation that substrate-supported generation of DeltaPsi(m) is impaired despite intact electron transport, make it likely that uncoupling plays a major role in the
mitochondrial dysfunction in proximal tubules during H/R.